This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from the inventor""s application SETTING METHOD FOR GAIN AND OFFSET VALUE IN LIQUID CRYSTAL DISPLAY filed with the Korean Industrial Property Office on Jun. 15, 1999 and there duly assigned Ser. No. 22398/1999.
1. Field of the Invention
The present invention relates to a system for adjusting gain and offset values for a liquid crystal display (LCD). More particularly, the invention concerns so adjusting gain and offset values for an LCD as to set the best-fitted offset value controlling the brightness of an image displayed on a screen and the best-fitted gain value of video signals, during an LCD production process. The invention also concerns a method of using the system.
2. Description of the Prior Art
LCDs are light in weight, unlike cathode-ray tube (CRT) monitors. LCDs can be manufactured to be quite thin while nonetheless displaying an image clearly without distortion. This has made LCDs particularly useful for notebook-type computers.
An LCD adjusts its white balance in accordance with the gain of red (R) green (G), and blue (B) color signals sent to the LCD from a computer system. The light and darkness of the LCD are varied for contrasting clearly a bright image and a dark image. To provide a given brightness value for an LCD panel, it is known to establish a cut off voltage according to a bias of the R, G, and B color signals displayed on the LCD panel. Brightness is varied by generating a bias voltage, standardizing the cutoff voltage in accordance with a desired adjustment of the brightness.
FIG. 1 is a block diagram showing a construction of a liquid crystal display according to the prior art. A computer system 1 simultaneously sends video signals (R, G and B color signals) for display on an LCD screen, as well as a horizontal synchronizing signal H and a vertical synchronizing signal V.
A pre-amplifier 2 amplifies the R, G, and B color signals from the computer system 1, in accordance with a brightness-control signal from a microcomputer 4. An analog-to-digital converter (ADC) 3 receives an analog video signal from preamplifier 2 and converts it to a digital video signal according to a divide value received from a phase locked loop (PLL) 5.
Microcomputer 4 detects and divides a horizontal synchronizing signal H and a vertical synchronizing signal V sent from computer system 1. The microcomputer determines an operating mode (e.g., color graphics adapter mode (CGA), video graphics array mode (VGA), and super video graphics array mode (SVGA)) through a frequency of a divided horizontal synchronizing signal H and a divided vertical synchronizing signal V, and provides a resolution in accordance with the operating mode so determined.
In this prior art system, the frequency and resolution of horizontal synchronizing signal H and vertical synchronizing signal V vary according to the selected operating mode. For example, in the CGA mode, the frequency of horizontal synchronizing signal H is 15.75 Khz, the frequency of vertical synchronizing signal V is 60 Hz, and the resolution is 640xc3x97350. In the VGA mode, the frequency of horizontal synchronizing signal H is 31.5 Khz, the frequency of vertical synchronizing signal V is 60 Hz, and the resolution is 720xc3x97350 or 640xc3x97480. In the SVGA mode, the frequency of horizontal synchronizing signal H is 35xcx9c37 KHz, the frequency of vertical synchronizing signal V is interlace and resolution is 800xc3x97600.
Therefore, microcomputer 4 sends a horizontal synchronizing signal H and a vertical synchronizing signal V to PLL 5 and a graphics controller 6, after recognizing a resolution according to the above-mentioned modes.
The PLL varies the divide value in accordance with the resolution recognized in microcomputer 4 and sends the divide value to ADC 3.
The graphics controller adjusts the frequency of a pulse signal from the ADC 3 through a horizontal synchronizing signal H from the PLL according to a resolution recognized by the microcomputer, so that a video signal is displayed on a LCD panel 7. The pre-amplifier, the ADC, and the PLL can be separated from one another or else integrated in a chip.
In order to adjust gain and offset values in a LCD of this prior art construction, R, G, and B analog color signals are sent to ADC 3 from pre-amplifier 2. These signals are fitted to a standard level of the ADC. A bottom level and a top level are adjusted in order to fit the R, G, and B analog color signals to the standard level of the ADC 3. To do so, a bottom level is set to adjust an offset value and a top level is set by adjusting a signal width to adjust a gain value.
In using this prior art system for adjusting gain value and offset value, an external apparatus (a xe2x80x9cJigxe2x80x9d) typically is connected to an output line of pre-amplifier 2 and ADC 3, so that an operator can adjust gain and offset values after visually inspecting an input waveform. Also, by programming the above-described adjusting operation, gain and offset values of an input waveform can be adjusted automatically without need for an operator actually to see an input waveform. The gain and offset values can be adjusted by reading a digital output value of the ADC and setting a bottom level to xe2x80x9c0x00xe2x80x9d and a top level to xe2x80x9c0xFFxe2x80x9d.
This prior art method for adjusting gain and offset values in a conventional LCD involves some inconvenience. A common environment must be established between an LCD and an external apparatus, since an operator must manually adjust gain and offset values by using his eyes.
Adjusting gain and offset values automatically by using a program also is a problematic. The best-fitted gain and offset values cannot readily be obtained, because all the area of a video signal to the ADC is considered and noise (ringing or damping phenomenon) is generated on an initial edge part of the video signal, as shown in FIGS. 2A and 2B, illustrating a waveform of a video signal to the ADC from the pre-amplifier, using the prior art system.
An object of the present invention is to provide an improved method for adjusting gain and offset values for an LCD. A further object is to obtain the best-fitted gain and offset values of R, G, and B color signals, by considering only stable area data in the waveform.
In order to achieve these objects, a method for adjusting gain and offset values for a liquid crystal display is provided. A first step is carried out for initializing a gain value to the maximum and an offset value to the minimum, in regard to gain and offset values of video signals from a computer system. In a second step, the offset value is adjusted through a comparison between the minimum data initialized in the first step and data of a video signal read by a base address register after setting the same for reading stable area data of a black area. The third step involves adjusting the gain value through a comparison between the maximum data initialized in the first step and data of a video signal read by a base address register after setting the same for reading a stable area data of a white area.
In a further embodiment, a method for adjusting gain and offset values for an LCD according to the present invention involves a first step of detecting a damping level of damping area data of a video signal from a computer system. A second step involves comparing the damping level of the damping area data detected in the first step with a damping level of damping area data stored previously in a microcomputer and deciding whether there is coinciding data. The next step involves, if there is coinciding data in the second process, setting the gain and offset data set at the damping level stored in the microcomputer, to gain and offset values in an LCD. The fourth step is, if there is no coinciding data in the second step, setting the gain and offset data set at the nearest damping level, to gain and offset values in an LCD. Then, gain and offset values are adjusted according to gain and offset values set in the third and second steps.